The incidence of insulin-dependent diabetes mellitus (IDDM) varies dramatically across racial groups and countries, with annual age-adjusted rates of more than 29/100,000 per year in Finland, but only 0.7/100,000 per year in Japan. Although reasons for these marked geographic differences are unknown, it is likely that genetic variations across populations are primary determinants of these incidence differences. To determine the contribution of genetic factors to the global patterns of IDDM incidence, international comparative studies are now being undertaken as part of the WHO Multinational Project for Childhood Diabetes, known as the DIAMOND Project. It is, therefore, necessary to develop and implement epidemiologic standards for these investigations which can be applied across populations. This will ensure that comparable data are obtained in all countries, and that relevant scientific questions can be properly addressed. The development of standards for molecular epidemiologic studies of IDDM is the objective of the NATO Advanced Research Workshop. During this meeting at the University of Pittsburgh, scientists from approximately 20 countries who are participating in the DIAMOND project will convene to discuss issues relating to the standardization of: 1) the collection of family history data to assess the risk of IDDM in first degree relatives, 2) case-control and family studies of the genetic determinants of the disease, and 3) laboratory methods and DNA technology transfer for the genetic marker evaluations. there will be presentations by key-note speakers, as well as invited contributions from all participants. After two days of presentations, individuals will assemble into working groups to discuss the implementation of these standards in countries across the world. The Workshop will conclude with the development of a uniform molecular epidemiologic approach which can be applied to IDDM and other chronic and autoimmune diseases. The results will be published as a volume in the NATO Advanced Science Institute Series and will serve as the standards for the DIAMOND Project. International comparative research based upon these standards will, therefore, permit an accurate evaluation of the contribution of genetic factors to the global patterns of IDDM incidence. By identifying factors responsible for the worldwide difference in IDDM incidence, it will be possible to begin to focus on preventive strategies, which is the ultimate objective of the DIAMOND Project.